1. Field of the Invention
The present invention relates to a circuit arrangement for a centrally-controlled, time-division multiplex telephone switching system wherein a central switching matrix network serves for call through-connection together with a central processor which serves for the control thereof, and wherein a plurality of decentralized terminal groups is each equipped with a switching matrix sub-network constructed as a time stage for the external connection of links and subscriber lines and for internal connection of link connecting paths leading to switching matrix network terminals of the central switching matrix network and each group is equipped with a decentralized control device for accepting switching characters from the lines, for preprocessing of switching characters, as well as for forwarding switching characters to the central processor and for sending switching characters onto the lines, and in which the terminal groups are respectively assigned to one another in pairs by two's, and within each of which connector units, for example subscriber lines, multiple subscriber connector circuits, multiple link terminating circuits and the like, serving, on the one hand, for external connection of the subscriber and/or link lines and primarily connected to the switching matrix sub-network within the respective terminal groups can be connected, first of all, to link terminating circuits individually serving for the internal connection of the link connecting paths and likewise primarily connected to the switching matrix sub-network within the appertaining terminal group. On the other hand, the connector units can be additionally connected, first externally and, secondly, internally to the switching matrix sub-network of the respective other cooperating terminal group, i.e. to a respective second terminal group, and vice-versa, whereupon, given a switching mode differing from separate operation of the appertaining, two terminal groups for connections that respectively proceed via a connector unit as well as via a link terminating circuit of the first or, respectively, second terminal group and via the switching matrix sub-network of the other terminal group, the corresponding processing of switching characters, as well as the setting of the switching matrix sub-network, is likewise carried out by the decentralized control device thereof with the assistance of switch elements, for example dial character receivers, dial character transmitters, ringing signal transmitters and call progress tone transmitters that can be occupied in a call-associated manner.
2. Description of the Prior Art
A circuit arrangement of the type set forth above is basically disclosed by the German published application 3 717 387. In a switching system of this type, therefore, the terminal groups are always allocated to one another in pairs. In the switching mode of a respective terminal group, their aforementioned connector units and their aforementioned link terminating circuits are respectively switchable to the switching matrix sub-network of the appertaining cooperating terminal group. By way of the latter, the switching operations are also then executed by way of assistance for that of the two terminal groups allocated to one another which is currently in the switching mode.
Among other things, there are a plurality of switch elements that can be occupied in a call-associated fashion for the call set-up that, among other things, serve the purpose of receiving dial characters and outputting call progress signals and also serve other purposes, as set forth above. Dial character receivers and call progress tone generators are notoriously known in this context. As mentioned, they can be occupied in a call-associated manner.